My home a/c unit will not kick on. When I drop the thermostat temp I hear a click on the outside unit and then it just makes a buzzing/humming noise. The start capacitor is the dual style but is not swollen at all. Its Sunday and no stores are open so it barrowed my neighbors capacitor (same size) and it does the same thing. Any other suggestions?

Have you checked,is there 220 volts at the contactor,, is the contactor doing the buzzing/humming?

Not sure what the contactor is. I just found out how to replace the capacitor earlier today. But the humming sounds exactly like the humming that occurs right before the fan and compressor typically come on.

I've got the same problem. I replaced my capacitor yesterday, and the unit kicked-on for a few minutes, but then stopped again with no fan and the buzzing - sounds like it is from the fan motor, and the fan is hard to turn by hand. With the power off, the fan turns freely.

Voltage from the red wire into the capacitor is 120V. Is that too low?

My fan motor was bad. Yours might be, too. Try to pinpoint the buzzing. If it's coming from the fan motor, that confirms it. I replaced mine today.